1. Field of the Invention
The present invention relates to a multilayer substrate with inner capacitors, which has capacitors, resistors and electric wiring conductor sections, and more particularly to a multilayer substrate with inner capacitors made by co-firing insulating layers and dielectric layers.
2. Prior Art
These days, a variety of electronic elements are being made smaller in size and mounted higher in density by use of semiconductor integrated circuit devices, such as ICs and LSIs. To cope with this trend, insulating substrates on which such semiconductor integrated circuit devices are mounted are required to be made smaller in size and higher in density. To meet these requirements, electric wires are being made thinner and multi-layered to increase density, and passive elements in electronic circuits, such as capacitors and resistors, are made in the form of chips. In addition, these miniaturized passive elements are attached to the electric wiring conductor sections provided on both sides of an insulating substrate, a practical use of both-side mounting of elements.
However, the significant advancement of semiconductor materials requires electric elements to be made far smaller in size and mounted far higher in density. The above-mentioned miniaturized passive elements, however, cannot fully meet the requirements.
To meet the requirements, a composite ceramic substrate has been proposed. The capacitor section (passive element) of this proposed substrate is printed as a thick film on an insulating layer (green sheet) by screen printing for example. Together with electrode sections and internal wiring conductor sections which are printed on the insulating layer by the same method as described above, the capacitor section is co-fired with the above-mentioned insulating layer. Other electric wiring conductor sections and resistor sections are then printed by the above-mentioned screen printing method on the insulating layer thus fired. The conductor sections and resistor sections are fired to obtain a hybrid composite ceramic substrate, thereby making electric elements smaller in size and higher in density. (Refer to Japanese Patent Publication No. 63-55795.)
In the case of this conventional composite ceramic substrate, when the dielectric layer made of a ceramics mainly comprising barium titanate (BaTiO.sub.3) for example is laminated with an insulating layer mainly comprising alumina which is high in mechanical strength, chemically stable and superior in insulation performance, and when the alumina ceramics of the insulating layer is co-fired with the ceramics comprising barium titanate of the dielectric layer, with the two ceramics being in contact with each other, these ceramics react with each other and the desired characteristics of the dielectric layer cannot be obtained. In addition, it is difficult to coincide the firing temperature of the ceramics comprising the alumina of the insulating layer with that of the ceramics comprising the barium titanate of the dielectric. layer. Furthermore, cracks are generated in the dielectric layer due to the difference in thermal expansion coefficient between the insulating layer and the dielectric layer, thereby reducing the insulation resistance and dielectric breakdown voltage of the capacitor section.